Pas de Conditionnel après 'si'

This is the error native French speakers notice immediately and judge harshly. Si je serais riche, je voyagerais — at first glance it might look fine to an anglophone. After all, English uses would in both clauses sometimes (If I would be rich, I would travel). In French, the rule is absolute and inviolable: the conditional NEVER appears in a si-clause. Not in modern French, not in classical French, not in any register or style. Si je serais is one of the most stigmatized errors in the language — French children are taught from primary school not to make it.

The mnemonic French teachers use to drum it into students is: Les SI n'aiment pas les RAIS. The si doesn't like the -rais endings (the conditional endings). It is a memory trick, not a rule of pronunciation, but it is hammered into French heads from age seven onwards. Anglophones who study French need to take that hammering on themselves, because the error is real and constant.

Once you have the rule, the reward is huge: French si-clauses are remarkably regular. Three patterns cover essentially every conditional sentence you will ever construct. This page lays out all three, then drills the negative rule until you cannot get it wrong.

The three si-patterns

French has exactly three si-clause patterns, each expressing a different degree of hypotheticality.

Pattern 1: Real / likely — si + present + future

When you describe a real, plausible condition — something that might genuinely happen — you use the present tense in the si-clause and the future in the main clause.

The future tense can be replaced by the present (especially in casual speech) or by an imperative, but the si-clause always stays in the present:

This pattern maps to English first conditional (If you come, we will go). The rule mirror is essentially identical between the two languages here.

Pattern 2: Hypothetical present — si + imparfait + conditional

When you describe a hypothetical, unreal, or unlikely present situation — if I were rich (but I'm not), if I had time (but I don't) — you use the imparfait in the si-clause and the present conditional in the main clause.

This is where the si je serais error lurks. The conditional belongs in the MAIN clause (je voyagerais), never in the si-clause itself. The si-clause must be in the imparfait (si j'étais).

Pattern 3: Counterfactual past — si + plus-que-parfait + conditionnel passé

When you describe a past situation that did NOT happen but you're imagining it had — if I had known, I would have come — you use the plus-que-parfait in the si-clause and the conditionnel passé (past conditional) in the main clause.

This pattern maps to English third conditional (If I had known, I would have come). Again, the rule is structurally similar in both languages — but the trap is that the conditionnel passé in French has a would have shape that learners are tempted to also put in the si-clause. Resist.

The rule that ties them all together

In all three patterns, look at where the conditional (or future) lives:

Notice: the si-clause always uses an indicative tense (present, imparfait, plus-que-parfait). The conditional and future never appear there. The main clause carries the future-ness or hypothetical-ness via future, conditional, or past conditional.

Why the rule exists

There is a coherent logic. Si introduces a hypothesis — a setup. The hypothesis itself is presented as a condition, not as something the speaker is committing to as fact. French signals this with an indicative tense that backshifts: present for real conditions, imparfait for hypothetical ones, plus-que-parfait for counterfactual ones. The backshift adds the hypothetical flavor.

The conditional, by contrast, marks the consequence — what would unfold IF the condition held. It is the response to the hypothesis, not the hypothesis itself. Putting the conditional in the si-clause would be like putting the consequence-marker on the cause: it confuses which is which.

English, more loosely, sometimes allows would in both clauses (If I would have known, I would have come) — but even in English this is widely considered substandard. French simply enforces the rule strictly: the conditional and the si-clause are never on the same side.

English transfer is the danger

The trap for anglophones comes from the way English sometimes uses would in if-clauses. If you would do me a favor — common, and acceptable in polite English requests. If I would be rich — substandard but not unheard of. If she would have known — common spoken English even though prescriptive English condemns it.

When anglophones translate these, they reach for the French conditional. Si tu voudrais me faire une faveur (wrong — should be si tu voulais bien me faire une faveur). Si je serais riche (wrong — should be si j'étais riche). Si elle aurait su (wrong — should be si elle avait su).

The cure: drop the would whenever you see if in your English thought, and ask yourself which French tense the situation calls for.

When you're tempted to use the conditional after si

There is one specific situation where anglophones reach for the conditional and are particularly likely to make this error: polite requests. In English, If you could send me the file and If you would send me the file are both polite forms. In French, the polite request uses the imparfait or the present, never the conditional, in the si-clause:

The temptation is strong because pourriez sounds polite and would be able matches English could. Resist. Use pouviez (imparfait) instead.

Si meaning whether — different rule

There is a version of si that is NOT conditional and DOES allow the future and conditional in the embedded clause. This is the si meaning whether, used in indirect questions.

This si introduces an indirect question, not a condition. It functions like English whether or if in I wonder if/whether. The rule that bans the conditional applies only to conditional si — the si of if.

A simple test: can you replace si with whether? If yes, you can use future or conditional. If no (it really means if), then you cannot.

This distinction is essential. Without it, learners over-correct and refuse to use the conditional after any si, even legitimate cases.

Mixed conditionals

French allows mixed conditionals where the si-clause and main clause refer to different time frames. The rules within each clause still apply: the si-clause uses imparfait or plus-que-parfait, never conditional; the main clause uses present conditional or past conditional.

In both cases, the si-clause respects its own rule (plus-que-parfait or imparfait) and the main clause respects its own rule (present conditional or past conditional). The mixing happens at the sentence level, not within either clause.

Style and register

The si-clause rule is enforced equally in all registers. There is no informal usage that licenses si je serais. From everyday conversation to literary prose, the rule holds. A single si je serais in a written text marks the writer as someone who has not mastered basic French grammar.

The one place you may hear hesitation is when a French speaker pauses, restarts, or self-corrects: si je... si j'avais... This is fine. It is the deliberate construction si je serais that is wrong.

Building the imparfait quickly

Since the si-clause for hypothetical present requires the imparfait, fluency depends on fast access to imparfait forms. The imparfait is built from the nous-form of the present (drop -ons, add -ais, -ais, -ait, -ions, -iez, -aient).

The imparfait is the workhorse of hypothetical conditions. Si j'étais, si j'avais, si je pouvais, si je savais — these openings should come fluidly, paired with their conditional counterparts in the main clause.

Common Mistakes

The errors below are the most frequent anglophone errors with si-clauses. The pattern is always the same: putting would (conditional) in the si-clause where French requires the indicative.

Key takeaways

The single most important rule in French si-clauses: the conditional NEVER goes in the si-clause. Memorize the mnemonic les SI n'aiment pas les RAIS. The si hates the -rais endings.

The three patterns cover everything:

• Si
  • present + future = real condition (if you come, I'll go)
• Si
  • imparfait + conditional = hypothetical present (if I were, I would)
• Si
  • plus-que-parfait + past conditional = counterfactual past (if I had been, I would have)

The si-clause always uses an indicative tense (present, imparfait, plus-que-parfait). The conditional and future tenses live exclusively in the main clause. There are no exceptions. There is no register where si je serais is acceptable.

The single biggest predictor of fluency in French conditional sentences is the speed at which you produce the si-clause without reaching for the conditional. Drill the imparfait of être, avoir, pouvoir, vouloir, faire, aller until si j'étais, si j'avais, si je pouvais are reflexes. Once those openings come automatically, the rest of the sentence falls into place — and the embarrassing si je serais error stays out of your mouth forever.